Developmental Dysplasia of the Hip
Developmental dysplasia of the hip (DDH) is a problem with the way a baby's hip joint forms before, during, or after birth — causing an unstable hip. In severe cases, the hip joint can dislocate or cause trouble walking.
Mild cases of DDH usually get better on their own as a baby grows. More severe cases may need treatment with a brace or surgery to reposition the hip and allow for proper healing.
At your baby's checkups, the doctor will examine the hips to look for DDH. Identifying and treating the problem early will help a child avoid muscle, joint, and skeletal problems down the road.
What Happens in DDH?
The hip is a ball-and-socket joint. The "ball" is the rounded top of the thighbone (the femoral head); the "socket" is a cup-shaped bone that the ball fits into (the acetabulum).
When a child has a mild case of DDH, the ball moves back and forth slightly in the socket, causing an unstable hip. In more serious cases, the ball becomes dislocated and moves completely out of the socket. In the most severe cases, the ball may not even reach the socket where it should be held in place.
Hip dislocations are fairly uncommon, affecting just 1 in 1,000 newborns. However, some degree of hip instability happens in as many as 1 in 3 newborns. Girls are more likely than boys to have hip dislocations.
The causes of DDH aren't completely understood, but experts think that many things are involved. A baby can be at risk for DDH due to:
- Bring cramped in the uterus. A fetus can develop DDH when there is less space to move inside the womb. This is more likely to happen in first pregnancies when the uterus is tight, or in pregnancies where there is less amniotic fluid in the womb.
- Breech position. Being in the breech position (buttocks facing the birth canal) can limit movement in the womb, especially when the baby's knees extend out with the feet near the head (called "frank breech").
- Other conditions. Babies born with conditions that are caused by their position in the womb, like metatarsus adductus (an inward curving of the foot), torticollis (stiff neck), and flat head syndrome (positional plagiocephaly), are more likely to develop DDH.
- Birth hormones. DDH also may be caused by an infant's response to the mother's hormones that relax the ligaments for labor and delivery, causing the baby's hip to soften and stretch during labor.
- Tight swaddling. After birth, swaddling a newborn too tightly around the hips can sometimes cause DDH. (When swaddled, a baby should still have some wiggle room for the legs, with hips and knees bent slightly and turned out.)
Signs and Symptoms
DDH usually affects only one side of the body, most often the left. Babies usually don't feel any pain and don't show any obvious symptoms. To diagnose it, doctors look for these signs:
- at birth, an audible "click" or palpable "clunk" during routine newborn checkups
- different leg lengths
- asymmetry in the fat folds of the thigh around the groin or buttocks
- after 3 months, asymmetry in the motion of the hip and obvious shortening of the affected leg
- in older kids, an exaggeration in the spinal curvature that may develop to compensate for the abnormally developed hip
- limping in older children
A doctor can determine whether a hip is dislocated or likely to become dislocated by gently pushing and pulling on the child's thighbones to see if they are loose in their sockets. In one commonly used diagnostic test, a child lies on a flat surface and his or her thighs are spread out to check the hips' range of motion.
A second test brings the knees together and attempts to push the femoral head out of the socket. It is during these tests that the doctor will hear a "click," which may indicate a dislocation. These maneuvers are done at routine checkups until babies are walking normally.
Sometimes a doctor will recommend an X-ray or ultrasound to get a better view of a dislocated hip. X-rays (which only take pictures of bones) are done with older kids, while ultrasounds (which take pictures of bones and soft tissues) are better for babies younger than 3 months old because their hip tissue has not yet hardened into bone.
Treatment for DDH depends on the child's age and the severity of the condition. Mild cases may correct themselves in the first few weeks of life. In many cases, however, the pediatrician will refer the child to see a bone specialist (orthopedic surgeon) for treatment.
If baby has an unstable hip that does not get better, a brace called a Pavlik harness will be used to hold the hip in position. This device keeps the femoral head in its socket by holding the knee up toward the child's head. A shoulder harness attaches to foot stirrups to keep the leg elevated. The goal is to keep the femoral head in the hip socket. As a baby grows, this helps the hip joint to develop normally. Treatment with the Pavlik harness lasts about 6 to 12 weeks, and continues until the hip is stable and ultrasound exams are normal.
Pavlik harnesses do not work in children over 6 months old. Kids who are older and continue to have DDH may need one of two types of surgery:
- A closed reduction, in which the surgeons gently put the hip back into place after the child is put under anesthesia. Then they put a cast on the body for 3-4 months to hold the bone in position. Doctors prefer this treatment in children under 18 months.
- An open reduction, in which the surgeons realign the hip and place the thighbone back into the hip socket. During the procedure, doctors loosen the tight muscles and tissues around the hip joint and then later tighten them once the hip is back in place. This is the best procedure for kids older than 18 months, or in cases when closed reduction doesn't work.
After reaching age 2 or 3, a child might need surgery on the pelvis to deepen the hip socket (if it's too shallow) or to shorten the thighbone or realign it. After surgery, kids need to wear a hip spica cast (a type of body cast that keeps the hips from moving). The cast usually is needed for several months, depending on the child's condition.
When DDH is recognized early and treated appropriately, most children develop normally and have no related problems.
DDH does not cause pain initially, but it may cause problems down the line, so it's important to treat it. Kids with untreated DDH end up having legs of uneven length in adulthood, and this can cause a limp or waddling gait, back and hip pain, and overall decreased agility.